1. Field of the Invention
The present invention generally relates to nuclear medicine, and systems for obtaining nuclear medicine images of a patient""s body organs of interest. In particular, the present invention relates to systems using semiconductor or solid-state detectors for obtaining nuclear medicine images by detecting radiation events emanating from a patient.
2. Description of the Background Art
Nuclear medicine is a unique medical specialty wherein radiation is used to acquire images which show the function and anatomy of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body, either by injection or ingestion, and are attracted to specific organs, bones or tissues of interest. Such radiopharmaceuticals produce gamma photon emissions which emanate from the body.
Conventional gamma cameras utilize a scintillation crystal (usually made of sodium iodide) which absorbs the gamma photon emissions and emits light photons (or light events) in response to the gamma absorption. An array of photodetectors, such as photomultiplier tubes, is positioned adjacent to the crystal. The photomultiplier tubes receive the light photons from the crystal and produce electrical signals having amplitudes corresponding to the amount of light photons received. The electrical signals from the photomultiplier tubes are applied to position computing circuitry, wherein the location of the light event is determined, and the event location is then stored in a memory, from which an image of the radiation field can be displayed or printed.
Also known in the art are solid-state nuclear imaging cameras, see, e.g., U.S. Pat. Nos. 4,292,645 and 5,132,542. Such cameras use solid-state or semiconductor detector arrays in place of the scintillation crystal and photomultiplier tubes. In a solid-state camera, gamma rays are absorbed in a semiconductor material, creating electron-hole pairs in the semiconductor material. A bias voltage across the semiconductor detector causes the electrons and holes to form an electric current through the semiconductor material. The currents are converted by associated circuitry into electrical signals, which are processed to determine the location and magnitude of the gamma ray absorption event. While solid-state cameras offer potential benefits over the conventional scintillation crystal cameras in terms of reduced weight, improved resolution, improved uniformity, and increased imaging area, the use of such cameras has presented its own set of problems. In particular, early solid-state detectors made of germanium had to be cryogenically cooled to achieve acceptable performance.
Semiconductor detectors made of cadmium zinc telluride (CZT) have recently been proposed for use in solid-state gamma cameras. Such detectors may be operated at room temperature. As shown generally in FIG. 1, a plurality of detector modules 10 are formed of CZT material, wherein each module is made up of an array of detector elements mounted to a circuit carrier 12 having a plurality of connector pins 14. Circuit carrier 12 can be a printed circuit board, or alternatively may encapsulate a number of integrated circuit chips. An example of a solid-state gamma camera using CZT detector modules is shown in U.S. Pat. No. 5,786,597.
One shortcoming of the prior art is that CZT detector modules require the application of a high negative voltage to the cathode side of the module. For large field-of-view applications, wherein such modules are arranged in a two dimensional array, conventional techniques of routing the high negative voltage to each modules, such as utilizing cables, introduce undesirable attenuation, which diminishes the performance characteristics of the camera.
There thus exists a need in the art for an improved high voltage distribution system for a solid-state gamma camera using semiconductor modules, and especially CZT detector modules.
The present invention solves the existing need by providing a solid-state gamma camera, including a plurality of semiconductor detector modules arranged in an array, each module having a cathode surface and an anode surface, a conductive strip in contact with the cathode surfaces of each of the plurality of detector modules, a high voltage electrode providing a high voltage supply to the conductive strip, and a pressure plate forcibly pressing the conductive strip in contact with the cathode surfaces of the plurality of detector modules.
According to another aspect, the invention provides a high voltage distribution system for distributing a high voltage supply to a plurality of semiconductor radiation detector modules, comprising a conductive strip connected to a high voltage supply, and contacting a surface of each of the plurality of semiconductor radiation detectors, a pressure plate for forcing the conductive strip into contact with the plurality of semiconductor radiation detectors by applying pressure to the conductive strip, and a vacuum source for creating a vacuum in an area occupied by said semiconductor modules and said conductive strip. According to yet another aspect, the invention provides a method of distributing a high voltage supply to a plurality of semiconductor radiation detectors as performed by the function of the distribution system.